There are animals that can generate energy through photosynthesis

The Eastern Emerald Elysia, a sea snail, the Pea Aphid, a plant eating insect, and the Spotted Salamander, a reptile that lives in USA and Canada can generate energy through photosynthesis because they have a special relationship with algae.

It seems that they either use the algae genes in their own cell so they simply welcome the algae in their body. This takes biology to a whole new level? Green men, here we come!
Via [SciShow].